1. Field of the Invention
The present invention relates generally to ceramic electronic components, and, more particularly, to a laminated ceramic electronic component formed by laminating ceramic layers and inner electrodes and a method for manufacturing the same.
2. Description of the Related Art
Recently, a market for mobile electronic devices, such as mobile phones, notebook personal computers, digital cameras, and digital audio devices, has been expanding. As these mobile electronic devices have been downsized and equipped with advanced functions, a demand for miniaturization and function enhancement of many laminated ceramic electronic components included in the mobile electronic devices is increasing. For example, there is a demand for miniaturization and larger capacitance of monolithic ceramic capacitors included in these mobile electronic devices.
To meet this demand, ceramic layers of the monolithic ceramic capacitors are being made thinner and the number of laminated ceramic layers tends to increase.
In general, at the time of manufacturing of a laminated ceramic electronic component, inner electrode patterns are printed on ceramic green sheets that serve as ceramic layers after firing to form inner-electrode-pattern arranged sheets. The inner-electrode-pattern arranged sheets are then laminated so that the inner electrode patterns on the sheets adjacent to each other in the lamination direction are in a predetermined positional relationship. The resulting mother block is cut at predetermined positions to obtain unfired ceramic element assemblies (raw chips). Generally, this ceramic element assembly has a structure in which a plurality of inner electrode patterns are arranged to face each other through unfired ceramic layers (ceramic green sheets) and one ends of the plurality of inner electrode patterns are alternately led out to opposite end surfaces of the ceramic element assembly.
Regarding the shape of the obtained unfired ceramic element assembly (raw chip), a center portion where the inner electrode patterns face each other through the ceramic layers tends to be relatively thick, whereas both end portions to which the inner electrode patterns are led out tend to be relatively thin. As the number of laminated ceramic green sheets increases, this tendency becomes more obvious. This phenomenon is caused by accumulated steps on the ceramic green sheets between a printed area with the printed inner electrodes patterns and a gap area without the inner electrode patterns.
There are following two main problems caused by the steps.
One is a problem regarding delamination (peeling) of ceramic layers that constitute the ceramic element assembly, which may undesirably reduce reliability of products.
The other is a problem regarding a mounting failure. Flatness of an upper surface of the chip is lost and holing of the chip using a sucking chuck undesirably becomes unstable.
To avoid this situation, a method for manufacturing a laminated ceramic electronic component that cancels a step of a gap area (hereinafter, also referred to as an “end gap area”) in a ceramic-layer longitudinal direction (direction along an inner-electrode led out direction) by increasing thickness of led-out parts of the inner electrodes has been suggested (see Japanese Unexamined Patent Application Publication No. 11-26279).
FIG. 11 is a sectional view showing a laminated ceramic electronic component manufactured using this method according to the related art. The laminated ceramic electronic component includes a ceramic element assembly 51 formed of a plurality of laminated ceramic layers 52, first inner electrodes 53a and second inner electrodes 53b that are formed inside of the ceramic element assembly 51, and a first outer terminal electrode 55a and a second outer terminal electrode 55b that are formed at end surfaces 54a and 54b of the ceramic element assembly 51, respectively. The inner electrodes 53a and 53b have effective parts 53a1 and 53b1 for obtaining a predetermined electric characteristic and led-out parts 53a2 and 53b2 led out from the effective parts to the end surfaces 54a and 54b of the ceramic element assembly 51, respectively. Thicknesses of the led-out parts 53a2 and 53b2 of the inner electrodes 53a and 53b are thicker than those of the effective parts 53a1 and 53b1, respectively.
FIG. 12 is a diagram showing a process for manufacturing a laminated ceramic electronic component according to the related art. FIG. 12 shows a state where a plurality of inner electrode patterns 63 are printed on a ceramic green sheet 60.
In the example shown in FIG. 12, the plurality of inner electrode patterns 63 each of which forms two inner electrodes when a mother block resulting from lamination is cut, namely, inner electrode patterns 63 each including two inner electrodes, are printed in a matrix on a surface of the ceramic green sheet 60 with center parts thereof (areas serving as the led-out parts after cutting) 63a being made thicker as shown in FIG. 12. In FIG. 12, cut lines are denoted by dotted lines D1 and D2. Here, a vertical-direction cut line extending vertical to the inner-electrode led-out direction is denoted by D1, whereas a horizontal-direction cut line that is parallel to the inner-electrode led-out direction and is vertical to the cut line D1 is denoted by D2.
In the related art, the ceramic green sheets 60 shown in FIG. 12 are laminated while alternately shifting the ceramic green sheets 60 in the direction parallel to the cut line D2 by one pitch of the cut line D1 to form a mother laminated body.
FIG. 13 is a schematic sectional view along the cut line D1 of the ceramic green sheet 60 shown in FIG. 12. As shown in FIG. 13, since each inner electrode pattern 63 is printed at predetermined intervals in the method according to the related art, a saddle phenomenon is caused, in which rising areas (elevated areas) 64 are formed near the periphery of each inner electrode pattern 63. As shown in FIG. 14, since the degree of rising of the rising areas 64 at ends of exposed parts of the inner electrode patterns 63 increases particularly in the design for thickening the led-out part of the inner electrodes, ceramic layers are more likely to peel off at the both ends of the exposed parts of the inner electrodes in a ceramic element assembly resulting from lamination, cutting, and firing of the ceramic green sheets having the inner electrode patterns formed thereon or a step is generated again because the rising areas accumulated in the lamination direction. As a result, reliability of products undesirably drops. Additionally, each side 63a extending in the ceramic-layer lamination direction located at the respective end of the exposed part of the inner electrode patterns 63 is not parallel to a lateral surface S of the ceramic element assembly but gaps are more likely to be formed between the neighboring ceramic layers. In that respect, the reliability is undesirably low.